fiendish vs hellish

fiendish and hellish both are adjectives.

Word	Noun	Adjective	Verb	Adverb
fiendish	No	Yes	No	No
hellish	No	Yes	No	No

As adjectives, fiendish and hellish are synonyms defined as:

fiendish and hellish: extremely evil or cruel; expressive of cruelty or befitting hell

Other synonyms of fiendish include demonic, diabolic, diabolical, infernal, satanic, unholy.

fiendish (adjective)	hellish (adjective)
extremely evil or cruel; expressive of cruelty or befitting hell	extremely evil or cruel; expressive of cruelty or befitting hell
	(informal) very unpleasant